'\" et
.TH PTHREAD_CANCEL "3P" 2017 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\"
.SH PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
.\"
.SH NAME
pthread_cancel
\(em cancel execution of a thread
.SH SYNOPSIS
.LP
.nf
#include <pthread.h>
.P
int pthread_cancel(pthread_t \fIthread\fP);
.fi
.SH DESCRIPTION
The
\fIpthread_cancel\fR()
function shall request that
.IR thread
be canceled. The target thread's cancelability state and type
determines when the cancellation takes effect. When the cancellation
is acted on, the cancellation cleanup handlers for
.IR thread
shall be called. When the last cancellation cleanup handler returns,
the thread-specific data destructor functions shall be called for
.IR thread .
When the last destructor function returns,
.IR thread
shall be terminated.
.P
The cancellation processing in the target thread shall run
asynchronously with respect to the calling thread returning from
\fIpthread_cancel\fR().
.SH "RETURN VALUE"
If successful, the
\fIpthread_cancel\fR()
function shall return zero; otherwise, an error number shall be
returned to indicate the error.
.SH ERRORS
The
\fIpthread_cancel\fR()
function shall not return an error code of
.BR [EINTR] .
.LP
.IR "The following sections are informative."
.SH EXAMPLES
None.
.SH "APPLICATION USAGE"
None.
.SH RATIONALE
Two alternative functions were considered for sending the cancellation
notification to a thread. One would be to define a new SIGCANCEL
signal that had the cancellation semantics when delivered; the other was
to define the new
\fIpthread_cancel\fR()
function, which would trigger the cancellation semantics.
.P
The advantage of a new signal was that so much of the delivery criteria
were identical to that used when trying to deliver a signal that making
cancellation notification a signal was seen as consistent. Indeed, many
implementations implement cancellation using a special signal. On the
other hand, there would be no signal functions that could be used with
this signal except
\fIpthread_kill\fR(),
and the behavior of the delivered cancellation signal would be unlike
any previously existing defined signal.
.P
The benefits of a special function include the recognition that this
signal would be defined because of the similar delivery criteria and
that this is the only common behavior between a cancellation request and
a signal. In addition, the cancellation delivery mechanism does not
have to be implemented as a signal. There are also strong, if not
stronger, parallels with language exception mechanisms than with
signals that are potentially obscured if the delivery mechanism is
visibly closer to signals.
.P
In the end, it was considered that as there were so many exceptions to
the use of the new signal with existing signals functions it
would be misleading. A special function has resolved this problem.
This function was carefully defined so that an implementation wishing
to provide the cancellation functions on top of signals could do so.
The special function also means that implementations are not obliged
to implement cancellation with signals.
.P
If an implementation detects use of a thread ID after the end of its
lifetime, it is recommended that the function should fail and report an
.BR [ESRCH] 
error.
.SH "FUTURE DIRECTIONS"
None.
.SH "SEE ALSO"
.ad l
.IR "\fIpthread_exit\fR\^(\|)",
.IR "\fIpthread_cond_timedwait\fR\^(\|)",
.IR "\fIpthread_join\fR\^(\|)",
.IR "\fIpthread_setcancelstate\fR\^(\|)"
.ad b
.P
The Base Definitions volume of POSIX.1\(hy2017,
.IR "\fB<pthread.h>\fP"
.\"
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1-2017, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, 2018 Edition,
Copyright (C) 2018 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
In the event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .
.PP
Any typographical or formatting errors that appear
in this page are most likely
to have been introduced during the conversion of the source files to
man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
